Using a newly developed quantitative electron density index, the heavy ion number, as a basis of comparison to X-ray CT scan data, represented by the Hounsfield number, we are beginning a systematic investigation of the properties of biologically important compounds and a variety of normal and abnormal tissues, including tumor specimens. The comparisons will be made on CT scans. Heavy ion radiography is sensitive in measuring electron density differences in a domain where X-ray absorbtion coefficients do not differentiate. Further work will be done on compensating for edge effects in heavy ion tomography. Clinical investigations on mammography, neuroradiography and therapy planning related radiography are continuing.